The present invention relates to a flame retardant, antistatic polyester resin composition, and more particularly to a polyester resin composition having excellent antistatic properties, flame resistance, heat resistance and mechanical strength and suitable for various uses, particularly as electric and electronic equipment parts.
Thermoplastic polyester resins, typically polyethylene terephthalate and polytetramethylene terephthalate, have been widely used as fibers, films, molding materials and the like, since they have excellent mechanical and electrical properties.
Reinforced thermoplastic polyester resin compositions have greatly improved mechanical strength and heat resistance and are obtained by incorporating a reinforcing filler such as glass fiber into these thermoplastic polyester resins. The reinforced resin compositions are suitable as a material for functional parts.
In recent years, a demand for fire safety increases more and more, particularly in the field of electric and electronic equipment parts, in addition to properties such as mechanical strength and heat resistance. Thus, investigation on flame retardation of resins has been made and flame retardant resin compositions incorporated with various flame retardants have been put on the market.
As to flame retardation of thermoplastic polyester resins, it is proposed, for example, to add a halogenated polystyrene resin (as disclosed in Japanese Patent Publications Kokai No. 50-92346, No. 4-198357 and No. 5-140427), to add a halogenated bisphenol A type epoxy resin (as disclosed in Japanese Patent Publications Kokai No. 50-35257 and No. 62-15256), and to add a high molecular weight halogenated bisphenol A type phenoxy resin.
On the other hand, it is known that thermoplastic resin compositions containing a polyester resin are easy to be charged. This tendency does not change even in the case of the above-mentioned flame retardants being incorporated therein. It is well known to add a conductive carbon black to the compositions in order to impart an antistatic property to the compositions, as disclosed for example in Japanese Patent Publication Kokai No. 49-99734.
However, in case that the antistatic property is imparted to flame retarded polyester resin compositions by incorporation of conductive carbon black, the resins are deteriorated by conductive carbon black, thus resulting in lowering of the mechanical strength. Therefore, it is required to use the conductive carbon black in an amount of as small as possible. On the other hand, the conductive carbon black has to be uniformly dispersed in the resin compositions. If the carbon black has not been uniformly dispersed, no desired electric resistance is obtained, and also a variation in electric resistance value generates. Further, the plastication characteristics of the compositions during molding processing does not become constant and, therefore, for example, in case of injection molding, the metering time is not stabilized, so flash and short shot nonuniformly generate in the obtained moldings, resulting in increase of fraction defective.
A general procedure which has been conventionally adopted to cope with uniform dispersion of conductive carbon black is to raise the number of rotations of a screw in extruder or other mixing machines and in molding to achieve a high degree of kneading. However, in that case, resins may be deteriorated by shearing due to the screw to remarkably lower the mechanical strength. Thus, it is desired that the mechanical strength is not lowered, even if a conductive carbon black is uniformly dispersed in thermoplastic resins to impart the antistatic property to the resins.
It is an object of the present invention to provide an antistatic thermoplastic polyester resin composition having high heat resistance, high mechanical strength and high flame retardancy.
A further object of the present invention is to provide a flame retardant, antistatic polyester resin composition, according to which a desired electric resistance value can be obtained by incorporation of a small amount of conductive carbon black while maintaining high heat resistance, flame retardancy and mechanical strength and, moreover, which has stable plastication characteristics, so the fraction defective can be remarkably reduced.
A still further object of the present invention is to provide a reinforced polyester resin composition to which a flame retardancy and an antistatic property are imparted by incorporation of a flame retardant and a conductive carbon black without impairing the physical properties such as mechanical strength.
These and other objects of the present invention will become apparent from the description hereinafter.